The present invention relates to devices for injecting medication and, more particularly, to devices for injecting two or more medications simultaneously.
Injection devices are known that hold two cartridges of medication. The medication is forced to flow from the cartridges, through a manifold and out a single cannula in fluid communication with the manifold. Injection of the medications is accomplished by inserting the cannula into the patient and causing the medications to be expelled therefrom.
It is medically desirable in the treatment of certain conditions of the human body to administer several types and dosage amounts of medication simultaneously. The treatment of diabetes is one such example. Different types of insulin act in different fashions. A fast acting insulin, such as for example a regular insulin, works quickly but for a short period of time after administration. A longer acting insulin, such as for example an isophane insulin, takes effect more slowly but for a longer period of time. It is therefore medically desirable to simultaneously inject both regular and isophane insulin when needed. In order to most accurately simulate the natural glucose curve of the body, the insulin user would need to inject different ratios or combinations of regular and isophane insulin at different times of the day.
One prior art technique of simultaneous injection of regular and isophane insulin is termed premixing. A syringe is loaded from separate vials of regular and isophane insulin by measuring and dispensing the insulin in a time-consuming and tedious process.
Also, the same is accomplished by preestablished mixtures of regular and isophane insulin that are packaged in a single vial or cartridge. The insulin user however, is constrained to use the preestablished mixtures and can not customize the ratios. The simulation of the natural glucose curve of the human body may require four injections per day. Each injection would require a different ratio of regular to isophane insulin.
The injection of a liquid medicine requires an amount of force necessary to overcome the static load on the plunger within the medication cartridge as well as the dynamic pressure as the liquid medication is forced to exit from a restricted opening. As the plunger moves, a continuous force is necessary to keep the plunger moving such that the desired dosage amount is ejected from the cartridge.